An electrical junction block or power distribution box is used in automotive vehicles to streamline wiring by eliminating multi-branch wiring. The power distribution box consolidates branch circuits and fuses, typically by incorporating bus bars into a housing to connect vehicle battery power to various electrical components serving the vehicle. The power distribution box often uses a stud bolt to connect a vehicle battery terminal to the bus bar.
In one type of conventional power distribution box, the stud bolt is molded into the plastic cover of the power distribution box. The insert molding process for joining the stud bolt to the cover, and the additional material needed, increases the manufacturing cost of the power distribution box and prevents replacement of a broken or stripped stud bolt.
A second type of conventional power distribution box shown in FIGS. 1 and 1A provides the stud bolt 140 as a separate component for direct attachment to a portion 100 of the power distribution box. Stud bolt holding features are molded into the plastic material of the box rather than insert molding the bolt into the box. Specifically, an open-ended, three-sided slot 100a is formed in the plastic wall of power distribution box housing 100, for example during the molding process. Slot 100a is sized to receive a square-headed stud bolt 140 in a radially sliding fit from the side of the housing. Sidewalls 100b and recessed platform 100c in slot 100a define the final resting place for stud bolt 140, engaging it in a close friction fit on three sides of the square head to prevent rotation. A bus bar 120 is subsequently assembled in essentially permanent fashion to housing 100, with a terminal portion 120a lying in slot 100 over bolt 140. An aperture 120b in bus bar 120 fits over the threaded shank of the stud bolt to radially secure the stud bolt in position. A battery terminal 160 is subsequently secured to terminal end 120a of bus bar 120 by being placed over the protruding threaded shank of the stud bolt, followed by a nut (not shown) threaded onto the bolt shank and torqued to compress terminal 160 against bus bar 120.
Although the radial sliding fit of stud bolt 140 in slot 100a is intended to permit the removal and replacement of stud bolts stripped or broken during assembly, the essentially permanent attachment of bus bar 120 to housing 100 makes this difficult.
Another disadvantage with the stud bolt holding arrangement of FIGS. 1 and 1A is that the plastic material of housing 100 directly absorbs any heat created by electrical arcing at the stud bolt. Arcing is often caused by insufficient torque on the nut securing the terminal to the stud bolt and bus bar. This can result in damage to the housing itself.
Insufficient torque generally results from the relatively low strength offered by slot 100a against the tendency of stud bolt 140 to rotate as the nut is applied.